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How do people exposed to the same extraordinary circumstances like an air crash or a terrorist attack react to these situations? Will they all suffer from post-traumatic stress disorder (PSTD) or will some cope better than others?

New research by Baycrest Health Sciences attempted to answer this question by studying memory and PSTD in a group of passengers, who years ago in an aircraft had stared in the face of death for 30 agonizing moments before they landed safely. The study has been published online this week in the journal Clinical Psychological Science.

On Aug. 24, 2001, an Air Transat flight bound for Portugal from Canada lost all power while flying over the Atlantic Ocean. It happened because of a leak in the fuel supply line due to which the aircraft lost all fuel. The passengers and crew, 306 of them, were told to prepare for a ditch in the sea, but after 25 minutes of high tension drama, the pilots were able to land the plane on an island with minimum casualties and no death. To understand the impact of this incident on the lives of the passengers, the researchers conducted personal interviews and psychological testing. This is the first study of its kind that analyzed the impact of a single event in the lives of several people.

The research was also aided by the fact that one of the authors was a passenger on the ill-fated flight. Dr. Margaret McKinnon was on her way to Portugal to celebrate her honeymoon when the incident occurred. She recalls that as the passengers were told to prepare for a sea landing, there was loss of on-board lighting and cabin depressurization.

"Imagine your worst nightmare — that's what it was like," McKinnon said in a statement. "This wasn't just a close call where your life flashes before your eyes in a split second and then everything is OK," she said. The sickening feeling of "I'm going to die" lasted an excruciating 30 minutes as the plane's systems shut down.

After the incident, McKinnon along with her colleagues, Dr. Daniela Palombo and Dr. Brian Levine, recruited 15 of her co-passengers on that flight, for the study. Since the researchers already had a first-person account of what had happened in the aircraft, they were able to probe both the quality and accuracy of passengers' memories for the AT emergency in great detail. The participants were also asked about two other events that had occurred in the same period. One was the Sept. 11, 2001 terrorist attacks and a neutral event. With this, they could determine if the passengers suffered from PSTD or not.

There were two key findings to the study:

First, Air Transat passengers could recall several details of the emergency. This is contrary to previous studies which state that people often try to block memory of traumatic events. Secondly, while passengers without PTSD could also recall the events on the flight, those with PTSD could recall a number of details that were external to the main event, like details that were not specific in time, or were repetitions or editorial statements, compared to passengers who did not develop PTSD and healthy controls.

This was observed even for the other two patterns tested, suggesting that it is not just the memory of the trauma that causes PTSD, but rather how a person processes memory for events in general.

"What our findings show is that it is not what happened but to whom it happened that may determine subsequent onset of PTSD," Levine said.

The inability to forget or block even minute details from a traumatic memory is related to mental control over memory recall, adding to other research that suggests altered memory processing may lead to PTSD.